The present invention relates broadly to apparatus for mixing a gas with a liquid, i.e., an aerator. More particularly, the present invention relates to an apparatus for aerating water in a water treatment process, and is an improvement of the apparatus discussed in U.S. Pat. No. 4,240,990, issued to Harold J. Inhofer et al. on Dec. 23, 1980, and U.S. Pat. No. 4,308,221, issued to Daniel J. Durda on Dec. 29, 1981, the disclosures of which are hereby incorporated by reference.
Aeration apparatus are utilized in the treatment of water for the purpose of increasing the dissolved oxygen (DO) content of the water. A certain amount of dissolved oxygen is required for the life of fish and other aquatic organisms. Dissolved oxygen is also required to prevent formation of offensive odors and to break down organic matter in water. The biochemical oxygen demand (BOD) is the measure of the amount of oxygen consumed in the biological processes which break down organic matter in water. A high BOD indicates that large amounts of organic waste are present and will use up large amounts of dissolved oxygen. Aeration apparatus are especially useful in increasing the amount of dissolved oxygen and, hence, are useful in high-BOD situation.
Aerators utilized in waste water treatment can be broadly classified into two types; a diffused air type, and a mechanical type. A diffused air type aerator introduces air or pure oxygen into water via submerged porous diffusers or nozzles. Mechanical type aerators agitate the water so as to promote solution of air from the atmosphere.
Mechanical type aerators are further classified as either surface aerators or turbine aerators. A surface aerator utilizes a submerged or partially submerged impeller which agitates the water vigorously to thereby entrain air in the water and cause a rapid change in the air-water interface. Turbine aerators generally utilize a rotating impeller which is disposed a certain distance below the surface of the water being treated. A draft tube is supported generally coaxial with the axis of rotation of the impeller and is utilized to supply air to the liquid adjacent the impeller.